A tieback system is a procedure for reconnecting a previously abandoned pre-production, exploration or appraisal well to a production platform or subsea christmas tree with the intention of producing hydrocarbons through it.
There are several advantages of using or being able to tieback to an existing well. For example, where an exploration well is drilled and finds a target that is particularly productive, it is possible to benefit from this prior work by tying back to an existing explorational well. This is particularly advantageous since it can save significant time and money rather than drilling another well with the purpose of production from the same field. A further advantage is that there are certain long lead times, such as incurred with the provision of a production platform or christmas trees etc, that are required to produce hydrocarbons. In addition, it is beneficial to drill production wells which can be temporarily abandoned during the time it takes to manufacture the platform etc. This then means that production can begin far sooner than it otherwise would have. Furthermore, at present certain wells, particularly in a high pressure/high temperature (HP/HT) environment cannot be tied back meaning that the well can only be drilled after the platform is in place.
In conventional tieback methods, a threaded connection is made between a well casing at the mudline and a well casing that extends towards the surface. The actuation of a threaded connection at this location can be restricted or even prohibited. In particular, within a HP/HT environment, nickel alloys are generally used within the well casings at this connection. However, nickel alloys have a strong tendency to scratch and gall one another under any sort of load. Accordingly, this present major problems when attempting to tie back within a HP/HT environment at the mudline.
It is an aim of the present invention to overcome at least one problem associated with the prior art whether referred to herein or otherwise.